Bone Morphogenetic Protein 9 (BMP9)

Growth differentiation factor 2 (GDF2) is a protein also known as bone morphogenetic protein (BMP)-9 that belongs to the transforming growth factor beta superfamily. It has a role in inducing and maintaining the ability of embryonic basal forebrain cholinergic neurons (BFCN) to respond to a neurotransmitter called acetylcholine; BFCN are important for the processes of learning, memory and attention. GDF2 is also important for the maturation of BFCN.

Another role of GDF2 has been recently suggested. GDF2 is a potent inducer of hepcidin  in liver cells (hepatocytes) and can regulate iron metabolism. The physiological receptor of GDF2 is thought to be activin receptor-like kinase 1, ALK1 (also called ACVRL1), an endothelial-specific type I receptor of the TGF-beta receptor family.